In the editorial, cardiologists James O'Keefe and Carl Lavie marshall the evidence suggesting that "extreme endurance exercise may exact a toll on cardiovascular (CV) health." The authors acknowledge that runners have only a very small risk of dying during a marathon, but "chronic extreme exercise" can induce "adverse structural and electrical remodeling, which offsets some of the CV benefits and longevity improvements conferred by moderate physical activity."

The authors cite data showing that "improvements from unfit to moderately fit confer dramatic reductions in morbidity and mortality" but that "fitness levels above 12 metabolic equivalents do not seem to translate into additional gains in CV health and longevity." The authors posit a U-curve, with "couch loungers" on one side and "extreme exercise aficionados" on the other side. They recommend moderate exercise as "the safe and comfortable zone at the bottom of the U curve, which, they say, is the sweet spot for most people. They conclude with a "take home message" recommending that most people limit vigorous exercise to 30-50 minutes per day.

In the WSJ article both O'Keefe and Lavie, former elite athletes with years of intense training, discuss their current moderate exercise regimens. The article also includes an old quote from Kenneth Cooper, the sports physician who helped launch the original aerobics movement: “If you are running more than 15 miles a week, you are doing it for some reason other than health.”

Update-- I asked Heart editor Adam Timmis to comment on this episode and whether he thought the Ingelfinger rule (which forbids prepublication publicity about a forthcoming paper) applied in this case. Here is the response I received:

"Embargo breaks are always regrettable, of course. But while the Ingelfinger rule is a worthy one, to apply it in this case would be like taking a mallet to a walnut.

The article in question was a review article- albeit in editorial format-not original research. And there is little or nothing in the piece that is not already in the public domain. Therefore, we think that it would be excessive to withdraw it from publication."